Context Navigation

From Luc Frauciel, "A few improvements to osgstereoimage:
- When using a large numbrer of files, the command line was too long;
Added a -files option that allow to store filenames in a file (one file
per line)
- Added some more intuitive key bindings for controls (left, right, + ,
-)
- Set the texture wrapping to CLAMP_TO_EDGE (it's cleaner now)
"